Combined primary feed for a radar antenna



Jan. 20,1970 u. VAN DER WAL ET AL 3, COMBINED PRIMARY FEED FOR A RADAR ANTEISNA Filed Oct. '1, 1968 N gvavrons AGENT Jan. 20, 1970 u, VAN D w. ETrAL- COMBINED PRIMARY FEED FOR A RADAR ANTENNA Fileq' Oct. 1, 1968 3 Sheets-Sheet 2 Fig. 3

INVENTORS UILKO VAN DER WAL MAXIMIUAAN H. BODMER y JAN NIJHUIS Jan. 20, 1 970 U, VAN DER w ET AL 3,491,362

COMBINED PRIMARY FEED FOR A RADAR ANTENNA Filed Oct. 1. 1968 3 Sheets-Sheet 3 Fig.4

INVENJQRS UILKO VAN DER m.

MAXIMILIAAN H. BODMER By JAN NIJHUIS US. Cl. 343-762 9 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a combined primary feed for a radar antenna and is more particularly concerned with a combined primary feed of the type comprising a throat portion which terminates in a flared horn having two narrow side walls, at least one of these narrow side walls being hinged at the throat of the horn, and driving means to move the hinged side wall either to the outside, to produce a large size aperture for pencil beam primary feed operation, or towards the center to provide a small size aperture for fan beam primary feed operation. A locking device locks the hinged wall at extreme positions, while a spring tends to move the wall to an equilibrium position. This equilibrium position is varied by a motor.

The present invention relates to a combined primary feed for a radar antenna and is more particularly concerned with a combined primary feed of the type comprising a throat portion which terminates in a flared horn having two narrow side walls, at least one of these narrow side walls being hinged at the throat of the horn, and driving means to move the hinged side wall either to the outside, to produce a large size aperture for pencil beam primary feed operation, or towards the center to provide a small size aperture for fan beam primary feed operation.

A combined feed of the above type provides a simple solution when the purpose of the radar indicates the desirability of having two diiferent beam patterns, to be used for different modes of operation or to be used alternately in successive revolutions of the radar antenna. Especially in the latter case it is required that the selection of the desired beam pattern is eifected in a very short time. Selection of either of the two beam patterns has been accomplished electrically by a solenoid or a drive motor. These prior art solutions have not been very satisfactory. It is therefore the principal object of the present invention to provide an improved combined primary feed permitting fast selection of either of two different beam patterns.

According to the invention this object and others are obtained by providing a combined feed of the type described with driving means comprising a member mounted for alternate rotary motion between a first and a second extreme position, a locking device including first means arranged to lock said member on reaching said first extreme position and second means arranged to lock said member on reaching said second extreme position, a spring assembly mounted to exert a varying torque on said member tending the latter to rotate to a stable equilibrium position intermediate between said first and second extreme position, means which in response to said member being locked in either of these extreme positions, operate on the said spring assembly to elfect a displacement of the stable equilibrium position such that the torque exerted on the locked member is increased to a predetermined value, means for releasing said member to rotate from its one to its other extreme position and means coupling said United States Patent ice member to said movable side wall, whereby the latter on release of said member is moved from its outside position to its center position or vice versa.

In a preferred form of the invention the said member consists of a main shaft carrying a crank, whilst further, using the central axis of the said throat portion as a reference, the said extreme positions are chosen such, that the said crank in either of these extreme positions will be approximately at right angles with the said central axis.

The invention and its advantages will be described in greater detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematic presentation of a horn feed having one movable side wall,

FIG. 2 is a schematic presentation of a horn feed in accordance with the invention,

FIG. 3 is a partial pictorial and schematic presentation of a possible embodiment of the driving means forming part of the horn feed shown in FIG. 2, and

FIG. 4 is a diagram used for the purpose of explanation.

Like reference numerals denote like parts in these figures.

FIG. 1 shows a horn feed that comprises a threat portion 1 formed by a waveguide having a cross-section whose shape and dimensions are determined primarily by the wavelength of the energy passing through the waveguide. This throat portion terminates in a flaring horn like portion 2 comprising fixedly positioned upper and lower narrow side walls formed by plates 3 and 4 and two fixedly positioned broad side walls formed by plates 5 and 6. In order that the aperture of the horn feed may be varied, this horn is further provided with an angularly positionable plate 7 which at its long sides is provided with suitable choke means (not shown).

Plate 7 is hinged at the throat portion of the horn feed and thus functions as a movable side wall.

The horn feed thus far described is well-known in the radar antenna art and is most frequently fixedly mounted at the focal point of a parabolic dish. If the horn feed has a relatively small aperture it produces a Wide beamwidth primary illumination lobe-pattern; and this pattern would illuminate the entire dish which would thereupon produce a narow beamwidth secondary illumination lobepattern. Conversely, if the horn feed has a relatively large aperture, it produces a narrow beamwidth primary illumination lobe-pattern, and this pattern would illuminate only the central portion of the dish which would thereupon produce a wide beamwidth secondary illumination lobe-pattern. In this Way, the horn feed at the focal point of the dish can produce either a broad fan beam or a narrow pencil beam secondary illumination pattern. From the previous discussion it will be evident that such an arrangement requires driving means to move the angularly positionable side wall, as required, either to the outside to produce a large size aperture or towards the center to provide a small size aperture.

According to the invention a particularly favourable and in every respect advantageous combined primary feed of the above type is obtained if the driving means comprise (see FIGS. 2 and 3) a member 8 mounted for alternate rotary motion between a first and a second extreme position 9, 10; a locking device 11 including first means 12 arranged to lock said member on reaching said first extreme position and second means 13 arranged to lock said member on reaching said second extreme position; a spring assembly 14 mounted to exert a varying torque on said member tending the latter to rotate to a stable equilibrium position intermediate between said first and second extreme positions, means 15 which in response to said member being locked in either one of its extreme positions operate on the said spring assembly to effect a displacement of the stable equilibrium position such that the torque exerted on the locked member is increased to a predetermined value, means 16 for releasing the said member to rotate from its one to its other extreme position and means 17 coupling said member to said movable side wall 7 whereby the latter on release of said member is moved from its outside position to its center position or vice versa.

In the preferred embodiment as shown in FIG. 3 the member 8 is constituted by a main shaft carrying a crank 18 which is fixedly connected to said main shaft. The crank is provided at its outer end with a hollow shaft 19 in which a spring-loaded and partially protruding pin 20 is slidably mounted. The main shaft and crank are mounted in a frame 21 permitting alternate rotary motion of the main shaft whereby the springloaded pin 20 is alternately locked by the means 12 and 13, which thus determine the first and second extreme positions 9 and 10, of said main shaft as will be discussed more fully below. The length of the main shaft is such that part of it protrudes from the frame 21. On this protruding end portion of the main shaft, the spring assembly 14 is mounted. In this embodiment the spring assembly comprises two schematically presented spiral springs 22 and 23 which are separately housed in chambers 24 and 25 of a spring drum. This spring drum is formed by a worm wheel 26 and two circular plates 27 and 28 which, by means of countersunk screws, such as 29, are fixedly connected to the worm wheel. The later is mounted for rotation about the .main shaft 8 and is further prevented from moving in the axial direction by means of rings 30 and 31 which are fixedly connected to the said main shaft. It should be noted that plates 27 and 28 are each provided with a centrally arranged circular hole, the diameter of which is slightly larger than the outer-diameter of the rings 30 and 31, so that the plates 27 and 28 will run clear of the rings 30 and 31 when the spring drum is rotated about the main shaft. Such rotation may be effected in one direction or the other by a correct energization the reversible twophase motor 15 (see FIG. 2) which drives the worm wheel 26 and hence the spring drum via a suitable transmission 32 and a driving worm 33.

The spiral springs are substantially identical. The outer end of each of these spiral springs is fixedly connected to the drum whilst the inner end of each one of these springs is fixedly connected, the one to ring 30 and the other to ring 31. In mounting said springs, they are pre-loaded to the same extent so as to apply opposing torques on the main shaft 8, tending the latter to rotate to a stable equilibrium position intermediate between the said first and second extreme positions 9 and 10.

Using now, the central axes 34 of the throat portion 1 as a reference, it may be observed that in the preferred embodiment as shown in FIGS. 2 and 3, the extreme positions 9 and 10 are chosen such, that crank 18 in either of these extreme positions will be approximately at right angles with said central axis 34. By positioning the rotatable spring drum 14, the stable equilibrium position of the main shaft can be adjusted so that it is located between said extreme positions 9 and 10. Since the opposing torques exerted on the said main shaft 8 are equal only for as long as the main shaft is in its equilibrium position, it will be clear that, when the main shaft is rotated out of its equilibrium position, a resultant torque will be exerted on the main shaft which thus tends to return to its equilibrium position. The rotary motion of the main shaft is used for driving the movable side wall 7. In the preferred embodiment shown, this is achieved by means of a connecting rod 17 coupling crank 18 with the movable side wall 7. This way of transferring the rotary motion of the main shaft 8 in conjunction with the chosen location of the extreme positions 9 and 10 is of particular advantage in that the torque required to move the main shaft out of a given extreme position is slight as compared to the torque actually exerted by the spring assembly. Thus, a

4 fast acceleration of the movable side wall on release of the main shaft, is ensured.

For the purpose of illustration FIG. 4 shows a rectangular coordinate system in which the varying and opposing torques exerted by each one of the spiral springs 22 and 23 is plotted as ordinate against the relative angular position of the main shaft 8 and spring drum 14 in degrees as abscissa. The stable equilibrium position of the main shaft is determined by the position of the rotatable drum 14. Therefore, if the stable equilibrium position is somewhere between the extreme positions in which the said main shaft becomes locked, the stable equilibrium position may be adjusted with respect to these extreme positions by rotating the spring drum. Accordingly, when the two extreme positions (see FIG. 4) are at 15 and 165 respectively and the stable equilibrium position is at 90, this stable equilibrium position can be shifted in either direction along the line L, which is the locus of the equilibrium positions, by rotating the spring drum in the one or in the other direction.

Assuming now, that the stable equilibrium position is chosen to be as shown in FIG. 4, that is to say, exactly centrally between the first and second extreme positions, and that the main shaft is locked in one of these extreme positions, it may be derived from FIG. 4 that the resultant torque then applied on the main shaft is equal to the difference of the torques applied by each one of the spiral springs. As shown this difference is equal to T or T,

depending on whether the main shaft is locked in its first or in its second extreme position. If there were no friction losses, this resultant torque would be just sufficiently large to rotate the main shaft, when released, from one extreme position to the other. The friction losses, however, are not negligible. Therefore, in order that the main shaft, when released, may indeed reach the other extreme position, the resultant torque should be increased to such a value that the friction losses are just overcome. Since the main shaft is locked in either of the extreme positions, the required increase in resultant torque can be obtained only by suitably displacing the stable equilibrium position with respect to the position centrally between the said first and second extreme positions. This may be effected by rotating the drum 14 in the proper direction through a predetermined angle.

If T in FIG. 4 is the resultant torque required to rotate the main shaft from its second to its first extreme position, the spring drum should be adjusted so that the equiiibrium position is at point A. Upon release of the main shaft the latter will rotate to be locked in the first extreme position. If, in order that the main shaft may return to the second extreme position, a resultant torque T is re quired, the equilibrium position should be at B. Hence, in the example of FIG. 4, each time the main shaft is locked, spring drum 14 should be rotated in the one or in the other direction through a predetermined angle of 55:70. Therefore, the moment the main shaft is locked, the circuit means for activating the said reversible motor 15 are closed. This motor then rotates the spring drum in the required direction through the said angle of 70.

After this rotation through 70 the said circuit means are automatically interrupted. The spring drum remains in the acquired position as the relatively high friction of the worm transmission 26, 32 prevents saiddrum from being rotated by the loaded springs. For simplifying the drawing, the circuit means for activating the reversible motor have not been shown. For closing and interrupting the said circuit means use may be made of micro switches that may be controlled by the movable side wall 7 and a cam disc (not shown) on the spring drum 14 respectively.

Upon release of the main shaft the static energy stored in the spring assembly is rapidly converted intokinetic energy. On reaching the equilibrium position all of the static energy has been converted into kinetic energy of the movable side wall 7. Owing to this kinetic energy the main shaft will pass through the point of equilibrium and will continue its rotation until all the kinetic energy is reconverted into static energy that is again stored in the spring assembly. Here it is important to note that by proper adjustment of the equilibrium position, it may be achieved that the point at which all of the kinetic energy is reconverted into static energy will just correspond with the extreme position in which the main shaft is to be locked. In this way, a smooth locking operation is ensured.

The means for locking the main shaft in its extreme positions and the means for releasing the main shaft may have any suitable form. In the preferred embodiment shown in FIG. 3 the locking device comprises a shaft 35 provided with an upper and lower ratchet 3'6 and 37 as well as a central ratchet 38. The shaft 35 is mounted for rotation in frame 21. The position of said shaft and the relative position of the upper and lower ratchets on said shaft is such that the main shaft 8 will be locked in either one of its extreme positions, due to the protruding spring loaded pin being locked by a tooth (such as 12 or 13) of either the upper or lower ratchet which thus functions as a catch. The upper ratchet co-operates with a spring loaded pawl 39, while the lower ratchet co-operates with a spring loaded pawl 40. The central ratchet 38 cooperates with a trigger mechanism. In the embodiment shown this trigger mechanism comprises a switch member which is mounted in frame 21 in a manner such that it is capable of performing a limited rectilinear movement in a plane transverse to the longitudinal axis of shaft 35. To this end the switch member 16 is provided with slide bars 41 and 42 fixedly connected to said member 16 at opposite ends and slidably mounted in associated guides 43 and 44 that are fixedly arranged in frame 21. The two extreme positions of the movable switch member each determine a switching position. The switch member may be set to either of these positions by energizing suitable driving means. For simplifying the drawings these driving means are not shown. It will be understood, however, that electromagnetic means such as, for instance, a solenoid may be used to act on the slide bars so as to thereby drive the switch member from its one to its other switching position. The switch member 16 comprises two stops 45 and 46 which alternately and in dependence upon the switching position of the switch member engage with a tooth of the central ratchet 38. The relative angular position of the teeth of the upper, lower and central ratchet are chosen so that the upper and the lower ratchet, alternately and in dependence upon the switching position of said switch member, will have one tooth in a position proper to engage with its associated pawl 39 or 40 and one further tooth in a position proper to engage with spring loaded pin 20, which by the torque applied on the main shaft is pressed against the said tooth. Therefore in either switching position the shaft 35 is prevented from rotating, in the one direction by a tooth of the central ratchet 38 and in the other direction by one of the pawls 39 and 40. During a switching interval shaft 35 is temporarily free to rotate through an angle of 60 and in a direction causing the release of pin 20 and hence of the main shaft 8.

To a man skilled in the art, it will be clear that the embodiment shown may be modified in several ways. In this respect it may be observed that the driving arrangement instead of driving a single narrow side wall might be used for simultaneously driving both narrow side walls. Further, the use of a connecting rod for coupling the main shaft with the movable side wall, though advantageous, is not essential, since especially with horn feeds of smaller size, the main shaft may very well be connected directly to the pin of the hinge, provided the movable side wall is rigidly secured to said pin. The spring assembly can also be modified, using, for example, one or two springs of a different type. Therefore it is to be clearly understood that the invention as illustrated and described in detail is by way of limitation; the spirit and scope of this invention being limited only by the terms of the appended claims.

What we claim is:

1. A combined primary radar feed of the type comprising a throat portion which terminates in a flared horn having two narrow side walls, whereby at least one of these narrow side walls is hinged at the throat of the horn, and driving means to move the hinged side wall either to the outside, to produce a large size aperture for fan beam primary feed operation, or towards the center to provide a small size aperture for pencil beam primary feed operation, wherein the said driving means comprise a member mounted for alternate rotary motion between a first and a second extreme position, a locking device including first means arranged to lock said member on reaching said first extreme position and second means arranged to lock said member on reaching said second extreme position, a spring assembly mounted to apply a varying torque on said member tending the latter to rotate to a stable equilibrium position intermediate between said first and second extreme positions, means which operate on the said spring assembly to effect a displacement of the stable equilibrium position such that the torque applied on the locked member is increased to a predetermined value, means for releasing the said member to rotate from its one to its other extreme position and means coupling said member to said movable side wall whereby the latter on release of said member is moved from its outside position to its center position or vice versa.

2. A combined primary feed as claimed in claim 1, wherein the said member consists of a main shaft carrying a crank, whilst further, using the central axis of the said throat portion as a reference, the said extreme positions are chosen such, that the said crank in either of these extreme positions will be approximately at right angles with the said central axis.

3. A combined primary feed as claimed in claim 2, wherein the main shaft and crank are mounted in a frame permitting alternate rotary motion of the main shaft, and wherein the crank is provided at its outer end with a hollow shaft in which a spring loaded and partially protruding pin is slidably mounted so as to cooperate with the first and second locking means which determine the first and second extreme positions.

4. A combined primary feed as claimed in claim 2 wherein the spring assembly comprises two spiral springs which are separately housed in a spring drum which is divided into two chambers by means of a worm wheel that is mounted for rotation about the said main shaft and is further prevented from moving in the axial direction by means of two rings which are fixedly connected to the said main shaft, the outer end of each of these spiral springs being fixedly connected to the drum whilst the inner end of each one of these springs is fixedly connected to an associated one of said springs.

5. A combined primary feed as claimed in claim 4, wherein the means for effecting a displacement of the stable equilibrium position are constituted by a reversible electric motor which upon being actuated rotates the said spring drum in the proper direction so as to thereby increase the applied torque to the said predetermined value.

6. A combined primary. feed as claimed in claim 2, wherein the said coupling means consist of a connecting rod coupling the said crank with said movable side wall.

7. A combined primary feed as claimed in claim 1. wherein the said locking device comprises a shaft carrying an upper, a lower and a central ratchet, the position of the said shaft and the relative position of the upper and lower ratchets on said shaft being such that the main shaft will be locked in either of its extreme positions due to the protruding spring loaded pin being locked by a tooth of either the upper or lower ratchet.

8. A combinedprimary feed as claimed in claim 7, wherein the means for releasing the said member is constituted by a trigger mechanism comprising a switch member which is mounted in the said frame in a manner such that it may perform a limited rectilinear motion in a plane transverse to the longitudinal axis of the shaft of the locking device, whereby the two extreme positions of this movable switch member each determine a switching position, said switch member comprising two stops which alternately and in dependence upon the switching position of said switch member engage with a tooth of the central ratchet.

9. An arrangement as claimed in claim 8, wherein the relative angular position of the teeth of the upper, lower and central ratchet are chosen such that the upper and the lower ratchet alternately and in dependence UNITED STATES PATENTS 12/1948 Risser et a1. 343786 9/1966 Randall et al. 343786 X RODNEY D. BENNETT, 111., Primary Examiner H. C. WAMSLEY, Assistant Examiner U.S. C1. X.R. 343786 

